Static electric machine.



J. B. DEMPSTBR. STATIC ELECTRIC MACHINE. APPLICATION FILED 00129, 1011.

Patented Sept. 1, 1914.

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JAMES B. DEMPSTER, OF DES MOINES, IOWA.

STATIC ELECTRIC MACHINE.

To all whom it may concern:

Be it known that I, JAMEs B. DEMPSTER, a citizen of the United States, residing at Des Moines, in the county of Polk and State of Iowa, have invented a certain new and useful Static Electric Machine, of which the following is a specification.

In static electric machines of the class in which a rotatable disk is provided made of insulating material such, for instance, as glass, it has been found that under certain conditions of temperature and humidity of the air moisture will condense upon the glass to such an extent as to permit a material leakage of electric current thereby impairing the eiiiciency of the machine.

My object is to provide a coating material for insulating surfaces of this class which coating material is inexpensive and may be readily, quickly and easily applied and which has non-hygroscopic properties capable of reducing the leakage of current to a minimum under all conditions of temperature and humidity of the air so as to materially increase the efficiency of the insulating surface to which the coating is applied.

My invention consists in the combination of the material and ingredients hereinafter set forth in a static electric machine, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims and illustrated in the accompanying drawings, in which:

Figure 1 shows a side elevation of a disk of insulating material such as glass provided with a coating of non-hygroscopic material embodying my invention ever part of its surface and a coating of a suitable binder such as shellac over another portion of its surface, and Fig. 2 shows an enlarged, detail, sectional view of a part of a glass disk provided with a coating material embodying my invention; the dotted line indicates the boundary of the part of the glass disk illustrated.

Referring to the accompanying drawings, I have illustrated a disk 10 of the kind usually employed in static electric machines for collecting the current. My invention applies only to the coating material, for use on the insulating surfaces of machines, such as static electric machines and it is therefore believed to be unnecessary to further illustrate and describe any of the Well known forms of static electric machines now in common use. In applying my invention to A Specification of Letters Patent.

Application filed October 9, 1911.

a glass disk of the class described, I first place on the surfaces thereof a coating of binding material 11 such as shellad' Be- Patented Sept. 1, 1914.

Serial No. 653,608.

fore the shellac has set and hardened I place on 1t a quantity of powdered Silica crystals 12 in such a manner that portions of the silica crystals that are adjacent to the shellac will become partially embedded therein, and I also manipulate the silica crystals in such a manner that the finer crystals thereof will enter between the larger crystals and come into engagement with the shellac so that substantially the entire surface of the shellac is covered by the irregular shaped crystals; then after the shellac has hardened the surface of the glass insulator will be substantially covered by the silica crystals, the major portion of each crystal being out of contact with the shellac binder so that the major portion of each crystal stands exposed to the air.

I have discovered that a glass disk of a static electric machine provided with a coating material embodying my invention will not be affected by moisture in the air and that there will be practically no leakage of current over the surface of the glass thus treated. On a glass or mica insulator disk for static electric machines I have found that when the disk is slightly colder than the surrounding atmosphere there will be such an amount of moisture condense on the disk as to permit the escape of an appreciable quantity of electricity, and I have also found that under similar conditions when my improved coating material is employed on the insulator disks, the quantity of leakage of the electric current will be materially reduced and will be in such quantities as to be scarcely appreciable to such an extent at least that the efficiency of a static electric machine, after my improved coating has been applied, is very materially increased over the efficiency of the same machine without my improved coating.

One of the advantages of having a coating material placed on the glass disks in crystal form is that by this means a larger surface is exposed to the air than would be the case with a perfectly smooth flat surface; hence the current eollecting efficiency of the static electric machine is increased and the leakage minimized on account of the form of my improved coating as well as on account of the properties of the material.

I do not desire to be understood as limiting my invention to the use of shellac as a binding material as it is obvious that any other Well known binding material that Will serve to permanently retain the silica crystals in position Will accomplish the same result. Furthermore I do not desire to be understood as limiting myself to the use of silica crystals for the reason that other crystals may have the same non-hygroscopic properties. Any other material that has the same herein described properties as silica Will, if capable of beingapplied in poW- dered crystal form, serve the same desirable function, regardless of the means for uniting it to the surface to be insulated.

I claim as my invention:

1. In a static electric machine, the combination of a current collecting plate, a

binder on the surface thereof, and a layer of small particles of non-hygroscopic crystals partially embedded in said binder.

2. In a static electric machine, the combination of a current collecting plate, a binder on the surface thereof, and a layer of small particles of silica crystals partially embedded in said binder.

3. In a. static electric machine, the combination of a current collecting disk, a coating of binding material thereon, and a coating of small particles of silica crystals partially embedded in said binder, for the purposes stated.

Des Moines, Iowa, August 12, 1910.

JAMES B. DEMPSTER.

Witnesses:

MARY VALLACE, W. A. LOFTUS.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, I). C. 

